1. Field of the Invention
This invention relates generally to the field of underwater remote load releases and more specifically to a machine for remotely decoupling coupled objects with a fusible link underwater.
2. Discussion of the Related Art
Devices for decoupling coupled objects, here termed ‘remote load releases’, are used in many different environments and industries. Among these remote load releases, many in use today are underwater ‘acoustic releases’, so-called because they are triggered remotely by an acoustic signal transmitted through the water. These devices are commonly used for the anchoring of scientific instruments or other payloads to the seafloor until their retrieval is desired. When the command-signal is received by the acoustic releases they release their anchors and float to the surface. The underwater environment presents many unusual challenges for engineers who use acoustic releases, such as environmental degradation including for example biofouling (marine growth) and electrolytic corrosion, the heat sink characteristics of water, high pressures, etc . . . This has resulted in two basic types of acoustic release design predominating in the industry and the patenting of other designs which are not as commercially successful.
Many acoustic releases have a motor or solenoid driven release mechanism. These are here termed ‘mechanical releases’. Typically, the motor or solenoid opens a gate or moves a piston, which then releases the load. Problems with this type of device include the bulk, cost, and frequent failure of the mechanism. When used in a marine environment, often environmental degradation such as marine organisms (biofouling) and electrolytic corrosion will jam the mechanism.
A second common type of acoustic release is frequently called a ‘burn wire release.’ This is actually a misnomer, because the device will not ‘burn’ a wire, but rather will corrode it slowly through electrolysis. A more accurate term for this is ‘electrolytic release’. This is a cost effective solution. However, problems are slow corrosion time (several minutes), corrosion speed dependence on water salinity (it will not work well in fresh water), and biofouling that can act as an electrical insulator, thus preventing efficient corrosion. The release is also limited to light loads, because it is difficult to corrode a heavy wire.
A third type is the “Thermal Release Device” in U.S. Pat. No. 4,430,552, to Peterson, issued on Feb. 7, 1984. This device uses an embedded heating element to melt a synthetic rope link; the combination of these items is called a ‘rope element’. Due to the slow rate at which the temperature of the heating element rises, this device requires insulation from the heat sink of the surrounding water. It also requires a DC to AC electricity converter (with its concomitant efficiency loss) to prevent premature corrosion of external electrical contacts. Another problem is that manufacturing time is relatively high for each rope element.
This Application discloses a thermal release device that does not require any such thermal insulation, and the heating element and the strength element are one and the same. As a consequence it is more simple, inexpensive, and effective.